1. FIELD OF THE INVENTION
The present invention relates to a protective system against a commutation failure in a chopper circuit and more particularly to a protective system against a commutation failure in a chopper circuit of an electrically driven vehicle, wherein means is provided for certifying the operative condition or validity of the protective system at any time desired.
2. DESCRIPTION OF THE PRIOR ART
When the thyristor chopper circuit in an electrically driven vehicle (hereafter referred to as EDV) fails in commutating action, an excessive current flows through the electric motor and there might be a danger of the EDV being uncontrollably driven by the excessive current. In order to avoid such a problem there is provided a protective system for preventing problems due to commutation failure. The protective system is adapted to disconnect the load or electric motor circuit from the power source as soon as a commutation failure has taken place. However, if there is a problem in the protective system, the protective system cannot cope with the commutation failure taking place during the movement of the EDV, so that a danger of uncontrollable drive will be caused. It is preferable to certify, before the start or during the travel of the EDV, whether the preventive system is in the properly operative or valid condition or not.
Conventionally, when it was desired to check the operative condition or validity of the protective system, an actual commutation failure was caused during the test of the protective system. This way of testing is, however, very inconvenient since the interval structure, e.g. electric wiring, nust be altered for that purpose.